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    <script>
        // var arr = [[1,2,3],[4,5,6],[7,8]];
        // console.log(arr[1][0]);
        // console.log(arr[0],arr[1],arr[2],arr[2][1]);

        // arr[2][2] = 9;
        // arr[2][0] = 77;
        // console.log(arr);

        var arr = [[1,2,3],[4,5,6],[7,8]];
        // 遍历多维数组
        for(var i = 0; i < arr.length; i++){
            // console.log(arr[i])
            for(var j = 0; j < arr[i].length; j++){
                console.log(arr[i][j]);
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        }

        console.log(arr.toString());

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